1. Field of the Invention
The present invention relates to an improvement of a discharge gas in a PDP(Plasma Display Panel), and more particularly, to a PDP filled with a mixture of three gases suitable for improvement of a composition of discharge gas which excites a fluorescent layer for displaying a color.
2. Discussion of the Related Art
Various forms of PDP's, driven in general by DC or AC and using an ultraviolet ray generated by a gas discharge, have been widely used, not only for display of characters, but also for display of images. It is known that the color display can be achieved by forming layers of different fluorescent materials in a discharge panel and exciting the layers with an ultraviolet ray generated by related gas discharge.
Typical type of PDP's using a surface discharge, such as the PDP shown in FIGS. 1 and 2 and the one as disclosed in U.S. Pat. No. 4,638,218 use various fluorescent materials for implementation of a color PDP. Basically, of one pair of substrates forming a sealed panel in such a color PDP, discharge electrodes 3, 4, 6 and 7 are provided only on a first substrate 1, while a top substrate 2 opposite to the first substrate 1 is provided with fluorescent layers 8, which will be excited by an ultraviolet ray generated by gaseous discharge, on an inside surface thereof, to emit a color light fixed by different fluorescent layers 8. The gas discharge electrodes are arranged on the top substrate 1 in X-, and Y-directions perpendicular to, and separated from each other. Surfaces of the electrodes 3, 4, 6 and 7 are coated with a protection layer 10 having a high secondary electron emission, such as MgO. This configuration prevents the fluorescent layers 8 from being degraded by direct impacts of ions generated in the discharge gas. Accordingly, such a configuration has been used until now for prolonged lifetime of the fluorescent layers.
As disclosed in U.S. Pat. No. 4,085,350, the discharge gases have been studied widely, which emits an ultraviolet ray for exciting the fluorescent layers to emit a visible light. It is known that a mixture gas of two gases(He+Xe), such as helium and xenon has been mostly used as a gas for displaying multiple colors in which color purities of lights have an important role. Xenon gas, known well as the penning effect, is used for lowering, not only a discharge sustaining voltage, but also a discharage initiating voltage. Heavy xenon ions in this gas give impact on a surface of magnesium oxide MgO coated on the electrodes. The magnesium oxide MgO layer is rapidly degraded by the ion impact, that shorten a lifetime of the PDP.
In a background art 3 component gas, the xenon gas is mixed in a fixed ratio of 0.2 vol %, at a gas pressure of 600 Torr. The fluroescent layer 8 used in this case is PIGI(Zn.sub.2 SiO.sub.4 :Mn) which is used widely and can be coated on all surface evenly. It is observed that a presence of argon gas over 5 vol % eliminates an orange color component from a neon gas discharge. The operation voltage rises when the argon gas present more than 80 vol %, with an increased driving circuit cost and an improved luminance effect. Therefore, a mixture gas He+Ar+Xr of three gases is used, in which argon gas, heavier than helium, is mixed with xenon gas for effective dropping of the xenon ion energy which give impact onto the surface of the magnesium oxide. However, the mixture gas He+Ar+Xr of three gases has a problem in that the mixture gas raises the operation voltage. A mixture of two gases(He+Xe) has been used for exciting one of R, G, B fluorescent materials and displaying a color. However, a neon gas dischrage degrades a color purity. In practical use, all the requrements of a long lifetime, a low operation voltage, a satisfactory luminance and a color purity for a PDP are important conditions. However, any of the background art have satisfied those conditions on the same time.